¹Zharkevich O.M., ¹Zhetessova G.S, ¹Pleshakova E.A., ²Utepova G

¹Karaganda State Technical University

²Karaganda State Industrial University

Pseudo alloyed coatings and their properties

Materials with pseudo alloyed structure are a special kind of composite coatings. They consist of materials which do not form solid solutions and compounds in liquid and solid state, i.e. they are different melting temperature and not alloyed together. Coatings combine the properties of each component due to the absence of any interaction of these materials to a great range of concentrations and temperatures. During application each of the particles are retained in the applied metal layer alone (Figure 1), although they were metallization in a molten state.

Figure 1 - The microstructure of the pseudo alloyed coating system Cu-Cr

Such coatings are called pseudo alloyed coatings. They are characterized by a number of important properties. This combination of high melting and evaporation with mechanical strength, hardness, damping capacity, high wear resistance (low friction coefficient), the ability to self-lubricating conditions in dry friction. Pseudo alloyed coatings have high electrical and thermal conductivity. Required properties pseudo alloyed coatings obtained by changing the ratio of the components. The same processes of manufacture: liquid phase, solid phase sintering, and impregnation properties substantially influence on pseudo alloyed coatings.

Coatings with pseudo alloyed structure can be prepared by methods spark alloying, ion-plasma magnetron sputtering and thermal gas (plasma, flame, electric metallization). A method of arc spraying is most prevalent during the application pseudo alloyed coatings, because offering high performance and manufacturability. Layer thickness may vary from 50 ... 100 microns to 3 ... 6 mm or more. The coating composition is adjusted by changing the wire diameter and feed rates (Figure 2).

1 – wire from sprayed metal; 2 - wires; 3 - mechanism for the wire; 4 - tips for wire; 5 - air nozzle; 6 - be plated detail

Figure 2 - Scheme of the spray head

Specific structure pseudo alloyed coating gives it high friction properties. Characteristic features of pseudo alloyed coating are heterogeneity and microporosity. The heterogeneity of the structure, the presence on surface roughness layer and pores (8 ... 12 vol. %) provide favorable conditions for preservation in the process of friction oil film even after lubrication. The mechanical properties of the coating pseudo alloyed connected with its structure. They depend on the process parameters, which change the shape and the number of occurrence oxide, particle size and shape. Thus, an increase of air pressure in arc spraying enables to obtain finer layer structure but causes substantial oxidation of the sprayed coating material. Spraying distance also has a great influence on the physical and mechanical properties of the coatings. At increase distance of 25 to 300 mm oxidation sprayed particles is increased and the amount of oxides in the layer increases from 10 to 40%. Moreover, sprayed particles reach the surface and therefore more cooled reduced coating strength characteristics.

Physical and mechanical properties pseudo alloyed coating can be improved by heat treatment, which is subjected to pseudo alloyed coating consisting completely of refractory metals or containing a predominant amount, as well as coating of the color pseudo alloys. Heat treatment may be subjected to the forest complex constructions that work with alternating loads, i.e. under stress in compression and tension. For such details are recommended thermal pretreatment and subsequent high-temperature tempering, i.e. sorbitizing.

Pseudo alloyed coatings not exclude preliminary thermochemical treatment. Such as cementation, i.e. the saturation of the carbon steel surface and subsequent spraying. Such pre-heat treatment should be carried out for low-carbon steels, which are used to manufacture heavy duty details, that is, experiencing alternating loads.

Pseudo alloyed coatings produced by the method of electric arc spraying, used as anti-friction material in friction slip have several advantages. Pseudo alloyed antifriction coatings well and quickly burnished and show less tendency to pilling compared to other anti-friction coatings. Using Cu-Pb as an antifriction coating material on the internal working surfaces of steel bushings is effective. Cu-Al coating with a mass concentration of copper 20% is recommended for sliding bearings operating in knots of metal-cutting equipment and handling devices.

Pseudo alloyed coating steel-Al is sprayed to improve the wear resistance of the pistons on their way to the surface of the arc. To improve the quality of the coating prior to application of pseudo alloyed layer is sprayed sub layer of aluminum, which is easily deformed under the influence of shrinkage stresses encountered in applying to it the pseudo-aluminum. This prevents the formation of cracks and enhances adhesion of the coating to the substrate.

The above data indicate the effective use of metalized pseudo alloyed coatings as anti-friction, wear-resistant corrosion-resistant materials.

Anti-friction pseudo alloyed coating is used in the manufacture of sliding bearings instead of bronze and babbitt to improve the working capacity of products in terms of abrasion as during the initial hardening.

References

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